The invention relates to a geared turbofan engine and a sun shaft for driving the sun gear of a planetary gearbox.
In geared turbofan engines—as used e.g. in aircraft engines—a fan stage is driven via a gearbox to reduce the rotational speed from the driving turbine stages. With a lower rotational speed of the fan stage the engine can operate more efficiently. The gearbox, e.g. a planetary gear box, with a sun gear and several planetary gears is subjected to large loads. The driving shaft of the gearbox, i.e. the sun shaft, requires some degree of flexibility at one end of the shaft and high stress resistance at the opposite end of the shaft, which can result in mutually contradictory design goals for the sun shaft. A sun shaft for this purpose is generally described in U.S. Pat. No. 7,824,305 B2.